ComboBox - Multi-column ComboBox When the option is Null

[gao]

Telerik UI for ASP.NET AJAX R2 2018.  When I use the AntiXssEncoder as the default encoder...
 web.config 
    <httpRuntime encoderType="Microsoft.Security.Application.AntiXssEncoder, AntiXssLibrary" maxRequestLength="102400"/>

A mistake as a figure